OK, when I was messing around on GTA 3 earlier, I was playing it after completing the game...Basically after completing the game you can mess around in the city and do some of the Missions over again, like this mission (The Diablos Turismo)... If I remember correctly (and this is going back almost 2 years now, to when I first completed the mission)... This mission is'nt part of the Main Missions of the game is it? I mean its one of the optionals isnt it? You can find out on gamefaqs if it is... Anyways if you are finding it difficult, just skip it and continue the Main Game